The clk_disable_unprepare() should be called in the error handling
of register_framebuffer(), fix it.

Fixes: 0937a7b3 ("video: ep93xx: Prepare clock before using it")
Signed-off-by: Gaosheng Cui <cuigaosheng1@huawei.com>
Signed-off-by: Helge Deller <deller@gmx.de>